perf(subscription): answer store_has_table from the index, not a scan

It runs once per datagram, for OBP and local traffic alike, and built a tuple
of every subscription to answer a yes/no question. Profiling a production
server at 198 datagrams/s put 67.8% of all CPU work inside it.

legs_in_table already reads the _by_table index and is on the port. Both were
added in the same commit as the scan, which never used them.

Constant time now instead of growing with the mesh: 6.8us to 0.30us at 120
subscriptions, 26.2us to 0.29us at 2400. On the server, 67.8% of work down to
0.84% and 42% less CPU at equal load.

src/adn_server/application/subscription/subscription_queries.py

@@ -26,8 +26,12 @@ from adn_server.application.ports import SubscriptionStore
 
 
 def store_has_table(store: SubscriptionStore, table_key: str) -> bool:
-    """True when the store has at least one leg in ``table_key``."""
-    return any(sub.table_key() == table_key for sub in store.snapshot())
+    """True when the store has at least one leg in ``table_key``.
+
+    Indexed: this runs per datagram, and the scan it replaces was building a tuple
+    of every subscription to answer a yes/no question.
+    """
+    return bool(store.legs_in_table(table_key))
 
 
 def system_has_active_leg_in_store(

tests/application/test_store_has_table_indexed.py

@@ -0,0 +1,99 @@
+# ADN DMR Peer Server - tests application store_has_table indexed
+#
+# Copyright (C) 2026  Rodrigo Pérez, CE5RPY <ce5rpy@qmd.cl>
+#
+###############################################################################
+#   This program is free software; you can redistribute it and/or modify
+#   it under the terms of the GNU General Public License as published by
+#   the Free Software Foundation; either version 3 of the License, or
+#   (at your option) any later version.
+#
+#   This program is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#   GNU General Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License
+#   along with this program; if not, write to the Free Software Foundation,
+#   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
+###############################################################################
+
+"""``store_has_table`` answers from the index, not from a scan.
+
+It runs once per datagram. Scanning every subscription to answer a yes/no
+question was 68% of the server's CPU at 198 datagrams/s. The index it now reads
+is maintained by upsert/remove, so these check it cannot answer from a stale one.
+"""
+
+from __future__ import annotations
+
+from adn_server.application.subscription.store_sync import replace_store_from_routing_table
+from adn_server.application.subscription.subscription_queries import store_has_table
+from adn_server.domain import bytes_3
+from adn_server.infrastructure.subscription_store import InMemorySubscriptionStore
+
+
+def _row(system: str, tgid: int, ts: int = 1) -> dict:
+    tg_b = bytes_3(tgid)
+    return {
+        "SYSTEM": system, "TS": ts, "TGID": tg_b, "ACTIVE": True, "TIMEOUT": 3600.0,
+        "TO_TYPE": "ON", "ON": [tg_b], "OFF": [], "RESET": [], "TIMER": 0.0,
+    }
+
+
+def _store(*tgids: int) -> InMemorySubscriptionStore:
+    store = InMemorySubscriptionStore()
+    replace_store_from_routing_table(
+        store, {str(t): [_row("OBP-A", t), _row("OBP-B", t)] for t in tgids}
+    )
+    return store
+
+
+def _by_scan(store: InMemorySubscriptionStore, table_key: str) -> bool:
+    """What store_has_table did before it used the index."""
+    return any(sub.table_key() == table_key for sub in store.snapshot())
+
+
+def test_it_answers_what_a_full_scan_answers() -> None:
+    store = _store(7305, 52090, 730444)
+    for key in ("7305", "52090", "730444", "9999", "", "0"):
+        assert store_has_table(store, key) == _by_scan(store, key), key
+
+
+def test_removing_the_last_leg_empties_the_table() -> None:
+    store = _store(7305, 52090)
+    assert store_has_table(store, "7305")
+
+    for sub in store.legs_in_table("7305"):
+        store.remove(sub.subscription_id)
+
+    assert store_has_table(store, "7305") is False
+    assert store_has_table(store, "7305") == _by_scan(store, "7305")
+    assert store_has_table(store, "52090") is True
+
+
+def test_removing_one_of_two_legs_keeps_the_table() -> None:
+    store = _store(7305)
+    store.remove(store.legs_in_table("7305")[0].subscription_id)
+
+    assert store_has_table(store, "7305") is True
+    assert store_has_table(store, "7305") == _by_scan(store, "7305")
+
+
+def test_a_replaced_store_forgets_the_old_tables() -> None:
+    store = _store(7305)
+    replace_store_from_routing_table(store, {"52090": [_row("OBP-A", 52090)]})
+
+    assert store_has_table(store, "7305") is False
+    assert store_has_table(store, "52090") is True
+    for key in ("7305", "52090"):
+        assert store_has_table(store, key) == _by_scan(store, key), key
+
+
+def test_it_does_not_get_slower_as_the_store_grows() -> None:
+    """The scan was O(n) per datagram; the index must not be."""
+    small = _store(*range(1000, 1010))
+    large = _store(*range(1000, 1400))
+    assert len(large.snapshot()) > 20 * len(small.snapshot())
+    assert store_has_table(small, "1005") == store_has_table(large, "1005")
+    assert len(large.legs_in_table("1005")) == 2